This invention, as expressed in the title of this specification, relates to a tub for a clothes-washing machine, in particular of the domestic type which houses a rotating drum inside which the washing load is placed; said washing tub consisting of a peripheral, cylindrical housing formed by a tub front-section and a tub rear-section which are joined together at their respective plastic material edges in order to enclose the drum in their interior by means of the fusion welding of the plastic materials of said edges, forming a weld bead between the front and rear sections.
The majority of the tubs existing on the domestic washing-machine market with moulded plastic washing tubs are joined by means of assembly with clips and/or screws. The joint is carried out by joining, by means of clips, the tub front section with the tub rear section, which incorporates the internal features, already assembled, such as the drum, the shaft, etc.
The joining of tubs by means of welding is not new on the market. Among the different welding techniques existing, the most commonly used is welding by vibration. Said vibration may be produced by means of ultrasonics or by friction, and the melting of the material at the joint is based on the application of pressure in order to produce close contact between the items to be welded. In comparison with the solution of tubs joined by means of clips, welded tubs allow the elimination of screws, clips and also the watertight seal, whose inclusion is rendered unnecessary.
Document EP 601 347 B1 discloses a washing-machine, or combined washing- and drying-machine, in particular of a domestic type, which comprises a plastic washing tub which houses a rotating drum within which the washing load is placed; said washing tub consisting essentially of a peripheral, cylindrical, integral housing, with a rear wall and a flange-shaped front wall which incorporates protrusions, moulded separately for their subsequent joining to protrusions on the front opening of the tub by means of the fusion welding of the plastic materials of which said protrusions are made.
Welding of the tubs is usually carried out by means of placing the flat sides of the protrusions face-to-face. The protrusions of the tub and of the front wall are L-shaped in section, and by means of welding, two edges of the protrusions are mutually joined. The pressure is exerted on both joined edges of the protrusions
Welding forms part of the group of permanent joints, but unlike others such as riveting or sticking, it provides certain advantages, such as the speed of manufacture, the high resistance of the joint, and the versatility of the joining process, applicable to a great number of materials and therefore appropriate for polymers or polymer-based compound materials, as is the case with current washing-machine tubs.